The present invention relates generally to panoramic imaging systems. More specifically, the present invention relates to a method and system for obtaining single and video, high-resolution, images of a panorama with a single viewpoint.
Large field-of-view (FOV) high resolution imaging systems have been a classical challenge for optical system design and engineering for decades. With a modern trend towards rapidly shirking pixel size and the rapidly growing number of pixels that are being packaged onto a single sensor, there have been enduring interests in both academia and industry for development of large FOV high resolution imaging systems. To address these needs the panoramic camera has recently risen as one of the top candidate technologies because of the increased FOV coverage and improved spatial resolution that they provide. However, while panoramic cameras provide advantages, they are rarely found in daily usage and practical applications because they are generally much more expensive and bulky than a conventional camera.
In addition to the practicality concerns, panoramic cameras suffer a number of design issues that inhibit their wide adoption for demanding imaging applications. Among one of those problems is the parallax error. A majority of panoramic cameras are unable to produce a seamless panoramic image because the viewing center of the system varies with the viewing directions. Secondly, serious imaging artifacts are commonly found in some panoramic cameras making them appear as if they had been imaged through a fisheye lens. Typically, those images are notoriously skewed, distorted and in certain cases, blurred towards the edge of the field. These artifacts get even worse as the FOV increases. All these issues have led to the degradation of optical quality and fidelity of panoramic images and, as a result, have limited the widespread application of panoramic cameras.
Past research efforts on panoramic cameras have been focused on resolving the above noted issues related to increasing FOV coverage, improving image resolution, reducing parallax errors and minimizing imaging artifacts. Although a lot of panoramic cameras have been proposed and developed in the literature, very few of them have achieved the same goal of devising a large FOV, high resolution, single viewpoint and minimization of artifacts using a relatively small form factor and practical package. A commonly adopted approach to large FOV high resolution panoramic imaging is to simply assemble a cluster of cameras each with smaller FOV and to direct each unit to a specified viewing angle, collecting a small portion of the entire scene. The multiple component images are then fused to achieve a large FOV panorama. A common problem associated with this approach is induced parallax errors. Since each component camera specifies a distinct viewpoint that is different from each of the others, the system is not of a single viewpoint. As a result a noticeable gap may arise near the boundary of two component images of the fused panoramic image.
A modification to this approach is to arrange camera arrays in a fashion that viewpoints of all component cameras are brought together, merging into a single viewpoint and leading to reduced parallax errors. In this approach, segmented mirrors are commonly used with each camera facing one segment of the mirror surface, the physical view centers of all component cameras are relayed into a common virtual view center, turning the camera cluster into a panoramic imaging system with a single viewpoint. The challenge associated with the mirror-based camera cluster method is that the mirror surface has to be carefully segmented without causing physical interference to either component cameras or blocking the view. Bending of light off the mirror surface also leads to increased system size, therefore resulting in a relatively bulkier and heavier system than a conventional single-sensor single lens camera.
Alternately, a curved mirror together with a single image sensor has been employed to create a so-named omnidirectional panoramic camera. In order to guarantee single viewpoint condition, the mirror is engineered mostly as a continuous surface with a specified shape and curvature. The incoming light is reflected off the mirror surface and redirected to a single viewpoint physically existing in space. An imaging camera is positioned at the viewpoint to capture the entire panorama at one shot. This approach, compared to a camera cluster, is simpler and less expensive. It requires only one camera instead of multiple image sensors. However, it suffers disadvantages similar to those of the fisheye lens approach, such as large distortion, low image resolution, as well as obscuration induced by the curved mirror. In general, most single sensor panoramic cameras suffer low imaging resolutions. Therefore, the present method and apparatus of the invention are most analogous to the camera cluster approach, whereas with capability of single viewpoint imaging and much reduced artifacts.
There is therefore a need for a method and apparatus for achieving single and video high resolution panoramic imaging over a hemispheric, spherical or near spherical FOV with a single viewpoint and reduced parallax errors.